Vehicles in use today may be powered by a wide-range of fuels such as leaded and unleaded gasoline, diesel fuel, methane and propane, to name a few. Whatever fuel is used to power a vehicle, the vehicle fuel system is specifically designed to continually supply fuel for the satisfactory operation of the engine. The fuel systems for the different fuels may vary from one another to account for the different properties of the various fuels.
For instance, some gasoline fuel systems, such as those used to supply fuel to marine engines, utilize a low pressure fuel pump disposed within the fuel tank to deliver fuel to a high pressure fuel pump downstream of the fuel tank which further increases the pressure of the fuel before delivery to the engine. Indeed, in some fuel delivery systems more than two fuel pumps may be used to provide fuel to the engine. Typically, at least one of the fuel pumps is electrically powered and thus, increases the power demand on the vehicle electrical system. Further, under at least some vehicle operating conditions, fewer than all of the fuel pumps in the fuel system may be needed to supply the engine fuel demand, and thus, operating all of the fuel pumps provides an unnecessary, excess fuel supply.
In propane fuel systems, the in-tank pressure of the propane is sufficient, at most operating temperatures, to discharge a pressurized propane supply from the tank into the engine for the satisfactory operation of the engine. However, the pressure of propane decreases dramatically at low temperatures and at about -40.degree. F. for some grades of propane, the pressure will be about 0 PSI. Thus, during these very low pressure conditions within the propane tank the supply of propane to the engine may be severely reduced if not terminated thereby adversely affecting the performance of the engine.